Determination of the optimal additive content for carbon nanotube (CNT) dispersion and the influence of its incorporation on hydration and physical-mechanical performance of cementitious matrices

Abstract

Carbon nanotubes (CNT) have gained great prominence due to their exceptional properties, such as high tensile strength and modulus of elasticity. However, one of the biggest difficulties regarding the use of CNT in cementitious matrices is their agglomeration tendency when added to concretes and mortars. An alternative to improve the efficiency of CNT dispersion in the matrix is the use of the dispersants (such as surfactants and additives based on polycarboxylate) with the use of an ultrasonic bath. Therefore, the aim of this work is to evaluate the effect of CNT incorporation and its influence on hydration (by means of calorimetry and X-ray diffraction) and on the physical–mechanical properties of the cementitious matrix. The results obtained pointed out that the multicriteria analysis is an efficient technique for determining the superplasticizer additive content used to disperse the CNT s and also that the presence of the properly dispersed nanoparticles accelerated the hydration of Portland cement but was not responsible for the formation of new phases. Significant differences were observed in the anhydrous and hydrated phases quantified in the cement matrix as a consequence of the amount of CNT used. It was also noted that the addition of CNT in a content equal to 0.075% led to statistically significant increases in compressive and flexural strength at 28 days of about 7% and 41%, respectively.